Client devices with wireless connectivity can generate the vast majority of data traffic on wireless networks today—typically as much as 90% on a 3G network. Most of this traffic may be generated by web browsing. With the widespread availability of multimedia content on the web and the emergence of popular multimedia-sharing sites, multimedia downloads and streams are growing dramatically faster than web browsing. In some networks, multimedia may have already surpassed browsing as the dominant form of traffic, overwhelming operators' networks.
Progressive download (PD) has become a popular technique to provide transport for network multimedia sessions. This simple mechanism effectively supports on-demand multimedia sessions over high capacity networks. A remote media player simply requests the download of a media clip, which is transferred and played progressively as audio and video frames are received at the player's end. In the Internet environment, this download is typically done over HTTP, which in addition provides effective firewall traversal features.
Progressive download, or pseudo-streaming (PS), is very effective when conducted over high-capacity networks such as the wired internet. In such an environment, it is assumed that the network connection can always be fast enough to meet or exceed the required download rate for the clip to play smoothly and without interruption. In other words, the network download rate can always be higher than the bitrate of the media file being downloaded. In addition, it is assumed that uncontrolled downloading of large media files may not affect other users sharing the network infrastructure. On the Internet, the abundance and predictability of network capacity allows for the use of uncontrolled downloading, in which as much of the media content as possible is downloaded as fast as possible.
A problem arises when progressive downloads are conducted over limited-capacity, time-variable, shared network links (for example, a wireless cellular connection). On such networks, the effective bandwidth a user sees changes with location and with the number of users sharing the same cellular infrastructure. In this environment, uncontrolled downloads of large files may result in network congestion. Moreover, multimedia servers may try to transmit media data to client devices at the highest rate permitted by the network. This may introduce bursts in traffic patterns, clogging the network and disrupting other users and applications.